1. Field of the Invention
The present invention provides an optical electro acoustic transducer for use in any acoustic string instrument, such as guitars, violins, string bass, cello, etc.
2. Description of the Prior Art
An acoustic guitar, one example of an acoustic string instrument, is a guitar that uses only an acoustic sound board. The air in this cavity resonates with the vibration modes of the string and at low frequencies, the volume of the sound generated increases or decreases depending on whether the air in the box is moving in phase or out of phase with the strings. The resonance interactions attenuate or amplify the sound at different frequencies, boosting or damping various harmonic tones.
No amplification actually occurs in this process, in the sense that no energy is externally added to increase the loudness of the sound (as would be the case with an electronic amplifier). All the energy is provided by the plucking of the string, the function of the entire acoustic system being to maximize intensity of sound.
An acoustic guitar can be amplified by using various types of pickups or microphones. The most common type of pickups used for acoustic guitar amplification are piezo and magnetic pickups. Piezo pickups are generally mounted under the bridge saddle of the acoustic guitar and can be plugged into a mixer or amplifier. Magnetic pickups are generally mounted in the sound hole of the acoustic guitar and are very similar to those found in electric guitars. An acoustic guitar with pickups for electrical amplification is known as an acoustic-electric guitar. New types of pickups have been introduced to try to amplify the full sound of these instruments, such as systems that include an internal microphone along with the body sensors or under the saddle pickups.
Most stringed instruments produce their sound through the application of energy to the strings, which sets them into vibratory motion. The strings alone, however, produce only a faint sound because they displace only a small volume of air as they vibrate. Consequently, the sound of the strings alone requires impedance matching to the surrounding air by transmitting their vibrations to a larger surface area capable of displacing larger volumes of air (and thus producing louder sounds). This calls for an arrangement that allows for the strings to vibrate freely, but also conducts those vibrations efficiently to the larger surface. A bridge is the customary means by which this is accomplished (a bridge is a device that supports the strings on a stringed instrument and transmits the vibration of those strings to some other structural component of the instrument in order to transfer the sound to the surrounding air).
Magnetic soundhole pickups exemplify the same functions as that of electric guitar pickups. Basically, they sense the movement of the strings of plain acoustic or acoustic electric guitars through a magnetic field.
Microphones are accurate transducers used to amplify both plain acoustic and acoustic electric guitars. They convert the sound produced by the guitar into electrical signals that are then picked up by amplifiers. In contrast with the magnetic soundhole pickups, microphones are more prone to feedback; as such, it is important that they are placed closely to the guitar, and that performers whose guitars have these transducers should have constrained motions. Despite the drawbacks of microphones, many musicians still prefer using these transducers because of their ability to pick up certain guitar sound characteristics such as high frequency and percussive sounds produced by tapping that cannot be picked up by other transducers.
Contact pickups are in direct contact with some specific parts of acoustic guitars. They pick up the motions taking place in the locations where they are installed and convert them into electrical signals that are then picked up by amplifiers. Almost all contact pickups use piezoelectric technology. Notable pickups that fall under this classification include the piezos, top pickups, and under-saddle pickups.
What is desired is to provide an acoustical transducer, or pickup, that has a more accurate reproduction to tonal quality of the instrument than provided by current piezo and magnetic pickups and more resistant to feedback than provided by microphones.